The afila (af) and tendrilled-acacia (tac)
genes radically modify leaf morphology of the pea (Pisumsativum
L.) plant and offer alternatives to the normal foliage type. The af_
gene, first described in 1965 (1), replaces leaflets with tendrils when present
in the homozygous recessive condition. The tac gene, isolated in 1972
following chemical mutagenesis with diethyl sulfate (3), restores small leaflets
to the tendrils of af plants when similarly homozygous. The resulting
af-tac phenotype (2) is characterized by a proliferation of tendrils
which terminate in either small, cup-shaped leaflets or leaflets similar in
shape but slightly smaller than those found on normal-foliage plants.

Despite world-wide use, the normal pea foliage type is known
to exhibit several disadvantages; e.g. a dense canopy that shades lower plant
parts, a reduction of light penetration into the understory and corresponding
decreases in photosynthetic activity of the lower leaves, a lack of color
uniformity of shelled peas due to shading, and a potential buildup of pathogens
due to reduced drying in the moist lower-canopy environment. Efforts to remedy
these disadvantages have resulted in adoption of the af foliage type in
many regions of the world. Despite the potential benefits that the tac
gene could offer the already-established af foliage type in the form of
increased photosynthetic area, there have been no studies which have evaluated
the potential utility of the af-tac gene combination. The
objective of this investigation was to evaluate the performance of af-tac
lines in comparison with af and normal foliage near-isolines in a range
of genetic backgrounds.

Included in the study were normal foliage, af foliage,
and af-tac foliage near-isogenic lines in three genetic
backgrounds: 'Alsweet', 'Frontier', and 'Dark Skin Perfection'. All near-isolines
were BC6-F5 derived. Four replications of a split-plot design were planted in
3.05 m linear plots along wire trellises in 1988 at Arlington, WI and in 1989 at
West Madison, WI and Arlington WI. In each experiment, genetic background was
assigned to the whole plot and foliage type was ascribed to the sub-plot. A 0.91
m section was removed from the plot center at the green pea harvest stage
(approximately 100 tenderometer), placed in an airtight plastic bag, and
transported to the laboratory at Madison, WI for analysis. Five plants were
chosen randomly from the harvest sample and separated for their constituent
foliage and yield components. In this way, yield components such as pods per
node, pods per plant, lowest pod-bearing node, peas per pod, and green pea yield
were recorded. The foliage components of a five-plant sample were bulked and
areas of stem, stipule, tendril, leaflet, and tac leaflet were measured
on a leaf area meter. These components were then dried for 48 h at 56°C and
weighed. Additional agronomic data measured included stand counts and dry seed
yield on a plot basis. Dry seed yield data were measured at Arlington in 1988
and 1989. Data presented in this report are means based on 9 observations from 9
harvestable replications: 4 at Arlington in 1988, 3 at Arlington in 1989, and 2
at West Madison in 1989. Dry seed yield data are means based on 7 observations
from only the Arlington locations. All statistical analyses were performed using
the GLM procedure of SAS.

Years and locations were designated 'environments'.
Comparisons among means were made with an LSD value at the 5% level.

Table 1. Mean performance of pea foliage types on wire
trellises averaged over three backgrounds and three environments.

Averaged over the three genetic backgrounds and three
environments, green pea yield of plants with af-tac foliage did
not differ significantly from af or normal plants on a per sample basis
(Table 1). Total number of pods, total foliage area, and total plant dry weight
were, however, higher for af-tac than af plants. Expression
of the tac gene varied significantly with genetic background. In Alsweet,
which has the earliest maturity of the three backgrounds, af plants
out-performed af-tac plants for most traits. The af-tac
combination in the Dark Skin Perfection background showed higher values for
nearly all yield component traits than the af or normal foliage types
(Table 2). Data which we have collected in other experiments suggest that,
unlike other foliage components, phenotypic expression of the tac gene
increases with plant ontogeny. Thus it seems likely that the tac
expression would reach its maximum and make its largest overall contribution in
performance in a late maturing background such as Dark Skin Perfection. This may
be due, though, simply to the greater number of nodes in the Dark Skin
Perfection background (data not shown). Dry seed yield data further illustrated
that the benefit of tac is realized with later maturity. Averaged across
backgrounds, more pronounced (though non-significant) differences were noted
between af-tac and af foliage types (Tables 1 and 2) at the
dry seed stage than were present at the green pea stage. In general, our results
of experiments conducted on trellises indicate that the af-tac
gene combination is equal or superior to the af type, and compares
favorably in performance to the normal foliage type. At present, the mid to
late-season cultivars should benefit most from the af-tac
combination. Dry seed yield data indicate that field pea cultivars and other
Pisum genotypes grown for their dry seed may be able to take full advantage
of the af-tac foliage type.